Refactor eureka related classes to separate module

[asafalima]

We wanted to remove the need for eureka from zuul-core for few reasons:

• We don't use it in our organisation, and like us there are others which use different service discovery solution.
• Eureka uses Jersey 1.x and JAX-RS 1.x which conflicts with our rest-sever which is based on Jersey 2.x
• Avoid unnecessary dependencies

To accomplish this goal I made the following changes:

• Created a new module zuul-eureka and moved any eureka related file to it.
• Added ServerStatusManager interface in core module and EurekaServerStatusManager implementation in the eureka module.
• Added ServerIpAddrExtractor interface in core module and DiscoveryServerIpAddrExtractor implementation in the eureka module which extracts the IP address from DiscoveryEnabledServer.
• Refactored out the out-of-service clients shutdown logic from ClientConnectionsShutdown to a separate class OutOfServiceConnectionsShutdown which resided in the eureka module.
• Remove DiscoveryEnabledServer related logic from RequestAttempt's constructor and moved it to the newRequestAttempt method in a new implementation of NettyOrigin: DiscoveryEnabledNettyOrigin which extends BasicNettyOrigin.

[asafalima]

@carl-mastrangelo @artgon I would really appreciate your input about this change.

[asafalima]

@carl-mastrangelo @artgon I need your help with pushing it forward

[artgon]

Hi @asafalima, this is a reasonable goal but this would break a lot of stuff for us internally. We are too coupled to Eureka and Ribbon in our internal Zuul.

We do have some future plans to address these coupling problems. Likely in the next major release of Zuul.

[mattnelson]

• Eureka uses Jersey 1.x and JAX-RS 1.x which conflicts with our rest-sever which is based on Jersey 2.x

@asafalima Eureka has jersey2 implementations available.

https://github.com/Netflix/eureka/tree/master/eureka-client-jersey2
https://github.com/Netflix/eureka/tree/master/eureka-core-jersey2

[asafalima]

Hi @artgon,

I saw @carl-mastrangelo indeed noted this as one of the goals for V3 in #771
Maybe we can make some changes to the work that was already done here to make it fit?